Andrew, Carl,
While discussing the input capacitors you have hit on a point concerning physical size -- "its a monster". In many instances two caps of the identical specs have greatly different physical dimensions. Has anyone every shown that the added area, in a film cap for example, contributes anything to the quality of the device. My only A to B comparison experience is with the sound of small SMD caps. They seem to sound very bright. I discovered this while constructing the first BPA300 chip amp.
Are boards going to be available for the amplifier?
Tad
While discussing the input capacitors you have hit on a point concerning physical size -- "its a monster". In many instances two caps of the identical specs have greatly different physical dimensions. Has anyone every shown that the added area, in a film cap for example, contributes anything to the quality of the device. My only A to B comparison experience is with the sound of small SMD caps. They seem to sound very bright. I discovered this while constructing the first BPA300 chip amp.
Are boards going to be available for the amplifier?
Tad
Andrew, Alex & Hugh,
Let's come together on a concensus as to what the input network and feed back cap amounts to. When we are done we need to have vendors and part numbers for the described parts. I suggest that 'DC in' amounts to a jumpers in place of the 47uF cap and the 12K resistor. Is that acceptable?
And are your favorite bypass caps for hanging off of the output collectors to ground? Suggestions? Thoughts?
Let's come together on a concensus as to what the input network and feed back cap amounts to. When we are done we need to have vendors and part numbers for the described parts. I suggest that 'DC in' amounts to a jumpers in place of the 47uF cap and the 12K resistor. Is that acceptable?
And are your favorite bypass caps for hanging off of the output collectors to ground? Suggestions? Thoughts?
A suggestion ...
Change the input cap that is now shown as 47uF be changed to a 4.7uF Wima MKS2 device. That fixes the input hi-pass to be 3dB down at 3Hz.
In the case of the cap in the feedback position, what if we specify it as a Nichicon MUSE? The 16 volt 220uF, 330uf and 470uf caps all have a 5mm pinout. The device diameter changes from 10mm to 12.5mm. I would simply plan for the larger diameter for those parties that want a larger cap in the feedback position.
Anyone have a preference for cap type for the 820pF device? Should it be box ceramic or silver mica?
Thoughts anyone?
Change the input cap that is now shown as 47uF be changed to a 4.7uF Wima MKS2 device. That fixes the input hi-pass to be 3dB down at 3Hz.
In the case of the cap in the feedback position, what if we specify it as a Nichicon MUSE? The 16 volt 220uF, 330uf and 470uf caps all have a 5mm pinout. The device diameter changes from 10mm to 12.5mm. I would simply plan for the larger diameter for those parties that want a larger cap in the feedback position.
Anyone have a preference for cap type for the 820pF device? Should it be box ceramic or silver mica?
Thoughts anyone?
Carl_Huff said:
Hi Carl, the original article explains why they used the components they did. Probably a good place to start.
"Some readers may wonder why we used such large electrolytic in the input and feedback networks. The answer is that we are acting to eliminate the effects of capacitor distortion in the audio passband ..... (and) to minimise the source impedance seen by the input transistors." (SC Aug 2008 )
Another 2 paras explain further in some detail.
Terry
it's not the size (value) that is the problem. I agree fully on the low impedance advantages.pheonix358 said:
The problem is the ratio between them.
Cin<= Rfb / Rin * Cfb / 1.4
Cin = 47uF is NOT LESS than 6.6uF.
The ratio must be sorted. Then you can play with values while maintaining the required ratio.
Tad,
The resistor that you refer to is specified to be 6.8 ohms at 1 watt. The schematic is posted back on post #167. The library part that I used in the layout is for a Vishay/Dale CW 3 watt part. The Mouser part number is 71-CW2B-7.5. The PCB thru holes are .047 inches (1.2mm) and are spaced 1 inch (25.4mm) apart. Similar parts equivalent to the one specified should work equally as well.
The resistor that you refer to is specified to be 6.8 ohms at 1 watt. The schematic is posted back on post #167. The library part that I used in the layout is for a Vishay/Dale CW 3 watt part. The Mouser part number is 71-CW2B-7.5. The PCB thru holes are .047 inches (1.2mm) and are spaced 1 inch (25.4mm) apart. Similar parts equivalent to the one specified should work equally as well.
Terry,
Before any of us spend the money to spin PCBs for a build, I need someone to check the PCB layout against the schematic to be sure that I haven't made a mistake. Would you be up for the task? I plan to check it again myself.
There is a free viewer on the Sprint Layout website. Sprint Layout viewer
Before any of us spend the money to spin PCBs for a build, I need someone to check the PCB layout against the schematic to be sure that I haven't made a mistake. Would you be up for the task? I plan to check it again myself.
There is a free viewer on the Sprint Layout website. Sprint Layout viewer
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